1. Technical Field of the Invention
The present invention relates to food products and their methods of preparation. More particularly, the present invention relates to sunflower seeds and to methods of hulling sunflower seeds involving contact with liquid gases at cryogenic temperatures.
2. The Prior Art
As is common in the industry, the term "sunflower" in the singular form is used herein synonymously to refer to sunflower seeds in a manner similar to "wheat" and "barley." Two types of sunflower are grown: (1) those for oilseed production, and (2) those for nut and bird food markets or non-oil sunflower. The oilseed varieties generally are black-seeded and have a thin hull that adheres tenaciously to the kernel. Seeds of the oilseed variety contain from 38% to 50% oil and about 20% protein. Non-oil sunflower also have been referred to as "confectionery" and also as "striped" or "large seeded" varieties. They generally have striped seeds and a relatively thick hull which is loosely attached to the kernel, permitting more complete decortication. Seeds of the non-oil varieties generally are larger than those of the oilseed types and have a lower oil content and test weight.
The term "decorticated" is used in its conventional sense in the sunflower industry to refer to the breaking or loosening of the shells from the seed meats to form a mixture of hulls and meats. The term "hulling" refers to separating the mixture into a hull fraction and meat fraction. Both confectionery and oilseed sunflower are typically mechanically decorticated and hulled in apparatus of basically two types: (1) percussion; i.e., the splitting of seeds by high speed impact, or (2) friction; i.e., the rubbing of seeds between two furrowed discs. Conventional mechanical sunflower decortication and hulling processes suffer from certain disadvantages. Milling plants are capital intensive. Moreover, milling frequently damages the sunflower meats. Also, mechanical decortication techniques do not insure complete removal of hull material from all seed meats.
While the problems and disadvantages of conventional mechanical decortication and hulling are common to both oilseed and confectionery varieties, oilseed sunflower is more difficult to process since the hull is bound more tightly to the seed than in confectionery sunflower. The problems associated with the more tightly bound shells are even more severe with the higher oil percentage hybrids. Oilseeds have nominal hull contents of 24-27% (by weight). While complete hulling would be desirable, conventional domestic oil expression processors typically find economical the removal of only about one third to two thirds of the hulls. Seed meats, hulls, and seeds tend to get broken into many pieces making separation or hulling difficult and therefore expensive beyond the above-indicated range. A significant amount of hull remains attached to meats as small silvers of fiber. Incomplete hulling also results in significant amounts of the wax layer intermediate the meat and hull undesirably entering the expressed oil. The wax is subsequently removed in conventional processing by, e.g., winterization, to provide a dewaxed oil of greater refrigerated stability.
Certain of the above limitations of mechanical milling are shared with certain other grains. Accordingly, the art has long sought non-mechanical methods to supplant or to improve mechanical milling of cereal grains and seeds. Thus, for example, various cereal grains have been treated, usually at elevated temperatures, with dilute sulfuric or hydrochloric acid solutions (U.S. Pat. No. 3,610,305, issued Oct. 5, 1971 to M. Suekane) or hydrogen peroxide (U.S. Pat. No. 3,520,340, issued July 14, 1970 to Y. Takeuchi) or lye (U.S. Pat. No. 3,358,723, issued Dec. 19, 1967 to R. P. Graham et al.) for hulling purposes. None of these methods have found widespread acceptance because of their numerous disadvantages such as requiring extended contact times, damage to or contamination of the seed meats or marginal utility. Mechanical milling of seed materials, and particularly including sunflower, remains the common hulling technique.
Applicants have discovered a surprisingly simple, quick and effective method of decorticating and hulling which is uniquely useful, it is believed, to sunflower. The presently discovered process involves infusing sunflower with a cryogenic liquid gas and thereafter heating the infused sunflower by contacting with a higher temperature heating medium. Of course, the brittleness of materials chilled to well below their glass transition temperatures with cryogenic gases is well known. However, it is highly surprising that sunflower can be uniquely treated to remove the shells from the seed meat without significant breakage of the seeds into nondecorticated pieces and without incurring the disadvantages of previous mechanical and non-mechanical hulling techniques. Unexpectedly, both oilseed and confectionery sunflower can be decorticated and hulled by the process of the present invention notwithstanding the known difficulty in decorticating and hulling the oilseed variety. Surprisingly, the hull splits cleanly into two halves which makes conventional downstream separation between the meats and hulls easier.
Furthermore, applicants have surprisingly discovered that the present process also removes the undesirable wax-like covering of the sunflower meat which tends to stay attached to loosened hulls. Generally, if performed at all, separate mechanical milling techniques have been used to remove or to "dewax" sunflower meats.
Cryogenic freezing, of course, has been used to freeze food products, both bulk and packaged. (See, generally, "Cryogenics," Encyclopedia of Food Science, ed. by M. S. Peterson and A. H. Johnson, The Avi Publishing Company, Inc., 1978, pg. 198-200). Carbon dioxide snow has been used to quick freeze food products in liquid or paste form. (U.S. Pat. No. 4,265,921, issued May 5, 1981 to A. Lermuzeaux). Recently, liquid gas, especially carbon dioxide, although not necessarily at cryogenic temperatures, has been used to decaffeinate coffee beans or to extract residual hexane from defatted soybeans (U.S. Pat. No. 3,966,981, issued June 29, 1976 to W. G. Schultz). Liquid nitrogen is the most commonly used cryogenic freezant. Liquid nitrogen food freezers are commercially available and generally operate by spraying or dribbling the liquid gas on the product, or alternatively, very cold vapor is passed over the product. None of the current commercial liquid nitrogen freezers employ the common laboratory practice of totally immersing a product for rapid cooling, e.g., a few seconds. Moreover, cryogenic cooling techniques are usually employed only with products which cannot be stored long at higher temperatures unlike grains or sunflower.